Better consideration of cumulative effects

27th January 2014

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Timothy Rimmer

Alexia Chapman, from AMEC, shares advice on how environmental impact assessment (EIA) practitioners can more effectively account for cumulative effects

One of the weakest aspects of EIA is the assessment of cumulative effects. Uncertainty over the potential cumulative impacts of projects can lead to significant delays in achieving consent.

Several guidance documents have been created to aid developers in undertaking EIA. However, advice on the cumulative impact assessment (CIA) process is limited with very little practical guidance on how to go about this.

As part of The Crown Estate’s enabling actions programme for the Pentland Firth and Orkney Waters (PFOW), a common approach was developed to facilitate the CIA process for wave and tidal current developments. This work is part of The Crown Estate’s PFOW cumulative impacts workstream. While this study was aimed at the wave and tidal energy developments in the PFOW, the outputs are likely to be relevant to developments across the UK not just offshore renewables.

The study found several issues that merited consideration and the development of a common approach. From reviewing a number of case studies it became clear that there were two key issues that frequently occurred; not starting the CIA early enough in the EIA process (i.e. during scoping) and a lack of clarity over what projects to include.


Early identification of potentially significant cumulative effects as part of the scoping process has often been considered to be too superficial in its nature given the lack of information that may be available at this stage. However, early identification of cumulative effects can be beneficial to the developer, as it can enable the potentially significant effects to be resolved in a timely and cost effective fashion. Scoping helps developers focus on the key impacts and makes the approach to CIA efficient and proportionate.

There can be drawbacks to identifying cumulative effects too early in the scoping process, however, and a practical project-specific approach needs to be adopted. Due to the often lengthy time between the initial identification of potentially significant cumulative effects (the scope) and an application being submitted, the CIA scope may change as new projects (or later phases of existing projects) enter the process and others are changed or abandoned.

The CIA scope should, therefore, be kept under review until the final design of the proposed development is identified. To prevent the process of deciding which developments should be considered in the CIA from lasting indefinitely, a final cut-off date needs to be established. This date represents that point in time which the gathering of data for CIA stops and the environmental statement is pulled together and written prior to submission. This needs to be set by mutual agreement between the developer and regulator.

What to include in CIA

One of the key questions to be asked is: At what stage in the planning process should a project be before it is included in CIA? As the legislation does not specify exactly which projects to include, several key documents have attempted to provide guidance on this aspect.

All guidance agrees that projects that have entered the planning process (i.e. that have at least submitted an application for consent) should be included where relevant or necessary. More recently, however, there has been the tendency to also include “reasonably foreseeable” future projects. Determining what is meant by “reasonably foreseeable” is difficult, however, and leaving the CIA open to include a wide range of projects that may never be implemented. This is especially pertinent in cases of emerging industries and novel technologies, where certainty as to whether a project will be constructed is less likely.

In reality, for an effective CIA to be undertaken, only projects with full datasets which have been adequately analysed and assessed can be included. Such information is only likely to become available once an application has been submitted. It is reasonable to suggest that it should be the responsibility of the competent authority to include in its scoping opinion any other projects which were submitted subsequently in the CIA process.

During the study it became clear that reasonably foreseeable projects could be defined as projects for which a scoping opinion has been sought and, where relevant, should be included in the CIA. However, only a qualitative assessment can be carried out on these projects due to the lack of available data.

Finally, this approach was developed using existing guidance, case study outcomes and considerable input from many stakeholders. CIA issues are being debated not just within the PFOW, but across several development areas in the UK, therefore any knowledge and learning gained will clearly aid the EIA process in the future.

This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.

Alexia Chapman is a senior consultant of marine ecology at AMEC.

The Crown Estate’s full report can be dowloaded from

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